This invention relates to a heating system for a dual-mode automotive vehicle, especially a bus, which is equipped to operate by means of either an electrical power source or an internal combustion engine.
Operation of such a vehicle is especially beneficial from the viewpoint of environmental protection. A known vehicle of this type, shown in German Pat. No. 2,311,190, has a heat exchanger which is constructed as a heat-storage block through which air is passed. This heat-storage block occupies a large amount of space and is very heavy. Furthermore, when the vehicle is standing (i.e., powered by neither the electrical power source, nor the internal combustion engine), the heat accumulator can be heated only by means of a cable or, alternatively, the accumulator can be taken off the vehicle and exchanged for a heated unit. This restricts the availability of the vehicle.
It is an object of this invention to increase the availability and operating radius of these vehicles, while maintaining maximal anti-pollution operating characteristics. Another object is to provide an electrically powered heat exchanger of small size and low weight which will be capable of supplying heat at the start of the operating, or heating-up cycle.
These and other objects are achieved in a heating system for a dual-mode vehicle (i.e., a vehicle which can be, powered by either electricity or an internal combustion engine) comprising an electrical heat exchanger, an auxiliary fuel heater, an electric water pump common to both electric heat exchanger and fuel heater, and control circuitry for energizing the heat exchanger when the engine cooling water temperature falls below a predetermined level. The electric heat exchanger includes a continuous-flow heater connected to receive a through-flow of cooling water from the engine. The continuous-flow heater comprises a tubular heat-exchanger having parallel connected tubes covered by vulcanized conductive sheaths which serve as heating elements. This heat-exchanger is capable of supplying a large amount of heat while occupying a relatively small space. The auxiliary fuel heater is connected in series with the continuous-flow heater and is operable only when the vehicle is not receiving power from the electrical power source. The electric water pump is connected for circulating water through both heaters and is operable at least during periods when the vehicle is standing.
Provision of the electric heat exchanger in a dual-mode vehicle ensures that the auxiliary fuel heater, which produces exhaust gases, need only be operated when the internal combustion engine is supplying power to the vehicle. Design of the heat exchanger as a continuous-flow heater which receives a through-flow of engine cooling water makes for an extremely efficient, small size-low weight apparatus which can easily be retrofitted to existing vehicle cooling systems.
Provision of the electric water pump ensures cooling water circulation through both electric and fuel heaters when the internal combustion engine is not running. Cooling of the engine, during relatively long periods of electric operation, is prevented by energizing the electric heater (even when no internal vehicle heat is demanded) to heat the cooling water. Thus, the engine exhibits a satisfactory exhaust characteristic immediately upon restarting.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawing which shows, for purposes of illustration only, an embodiment in accordance with the present invention.